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# File 'lib/color_decomposition/color/comparator.rb', line 5
def ciede2000(lab1, lab2)
lch1, lch2 = to_lch(lab1, lab2)
l_bar = (lch1[:l] + lch2[:l]) / 2
c_bar = (lch1[:c] + lch2[:c]) / 2
h_bar = mean_hue(lch1, lch2)
l_delta = lch2[:l] - lch1[:l]
c_delta = lch2[:c] - lch1[:c]
h_delta = hue_angle(lch1, lch2)
o_delta = 30 * Math.exp(-((h_bar - 275) / 25)**2)
t = 1 - 0.17 * Math.cos(radians(h_bar - 30)) +
0.24 * Math.cos(radians(2 * h_bar)) +
0.32 * Math.cos(radians(3 * h_bar + 6)) -
0.20 * Math.cos(radians(4 * h_bar - 63))
rc = 2 * Math.sqrt(c_bar**7 / (c_bar**7 + 25**7))
sl = 1 + 0.015 * (l_bar - 50)**2 / Math.sqrt(20 + (l_bar - 50)**2)
sc = 1 + 0.045 * c_bar
sh = 1 + 0.015 * c_bar * t
rt = -Math.sin(radians(2 * o_delta)) * rc
Math.sqrt((l_delta / sl)**2 + (c_delta / sc)**2 + (h_delta / sh)**2 +
rt * (c_delta / sc) * (h_delta / sh)).clamp(0, 100)
end
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